Embodiments of the inventive concept relate generally to semiconductor memory devices. More particularly, embodiments of the inventive concept relate to a semiconductor memory device comprising sense amplifiers configured to stably amplify data on a bitline pair.
A semiconductor memory device typically comprises a memory cell array comprising plurality of memory cells. The memory cells are typically arranged in rows and columns connected to corresponding wordlines and bitlines, and the memory cells are generally programmed and read by applying appropriate voltages to selected wordlines and bitlines and/or sensing voltages on the wordlines and bitlines.
To select the wordlines and bitlines for program and read operations, the semiconductor memory device receives a memory address and decodes the address to produce a row address and a column address. The row address corresponds to one or more selected wordlines and the column address corresponds to one or more selected bitlines. A program or read operation is then performed by applying program or read voltages to the selected wordlines and bitlines.
In some semiconductor memory devices, each bitline comprises a pair of signal lines carrying signals with a voltage difference. Such a pair of lines is called a bitline pair. In some devices, the two lines in a bitline pair carry complementary signals, such as a logical ‘0’ and a logical ‘1’.
A sense amplifier circuit is often used to sense and amplify the voltage difference between bit line pairs in a device. The sense amplifier typically receives a supply voltage and a ground voltage from a power supply circuit adjacent to the memory cell array. These voltages can be used to amplify the voltage difference between bitline pairs.
Bitline pairs are generally precharged to a predetermined voltage level before a sensing operation is performed by the sense amplifier circuit. Where the sensing operation is performed, the voltages on the bitline pair change in accordance with data stored in one or more memory cells being sensed. These changes on the bitlines generally cause the lines in the bitline pair to be driven to the supply voltage or the ground voltage through driving circuits or switches in the sense amplifier. These driving circuits may be implemented, for instance, by n-type and/or p-type metal oxide semiconductor (NMOS or PMOS) devices.
Unfortunately, in many devices, the driving capability of the driving circuits may vary. These variances can cause errors in sensed data, including bitline pairs with erroneously reversed polarity.